The present invention is directed to the reduction of distortion in a projected image, and more particularly to the use of a deformed mirrors in optical systems.
Distortion in a projected image can be reduced by the use of a compound correcting lens, contorted mirrors, computer image generator, or a scan converter. The latter two are complicated and costly, although they have the advantage of application to cases of severe distortion as easily as to cases of moderate distortion. The lens approach is also costly to develop, since the correction system has to be carefully designed to avoid introducing other aberrations. The mirror approach is relatively simple and inexpensive to implement and can be made dynamic (i.e., variable in time) as well. An example is the deformed mirror which is used with the light valve projection system described in Air Force report documentation AFHRL-TR-81-27(I).
Carefully deformed mirrors are finding frequent use in adaptive optical systems to reduce distortions in wavefronts. The general idea is to use the deformation to compensate for the phase distortions carried by the incident waves. An example occurs in the high powered lasers that launch beams into the atmosphere; here the backs of the large mirrors have arrays of servo-driven actuators that deform them to compensate for distortions in the wavefronts produced by fluctuations in atmospheric density along the beam path. The use of purposely deformed mirrors is the inverse to the situation in large space telescopes where servos are used to remove the deformations that occur because of the reduced gravity.
In adaptive optical systems, feedback loops are used to dynamically adjust the mirror deformation and adjust for the distortion caused by atmospheric inhomogeneity.
In general, the known prior art techniques employing deformable mirrors are employed to provide only phase compensation to the incident radiation wave. Thus, for example, fluctuations in atmospheric density cause phase distortions in the laser wave, and the deformed mirror is adapted to correct for these phase distortions. Insofar as is understood by applicants, however, these prior art devices are not employed to provide direction compensation to the projected light rays.
It is, therefore, an object of the present invention to provide a deformable mirror system adapted to provide direction compensation for distortion in a projected image.
Another object of the invention is to provide a prescription for determining the optimal shape of a mirror to reduce distortion in a projected image.
A further object of the invention is to provide a prescription for stressing a flat mirror to provide the optimal shape for reducing distortion in a projected image.
Yet another object of the present invention is to provide a system employing a dynamically deformable mirror for reduction of distortion in a dynamically projected image.
Another object of the invention is to provide a distorted mirror system adapted to minimize the distortion in an image projected from an oblique angle onto a curved surface, from a normal angle onto a curved surface, or from an oblique angle onto a flat surface.